FR2963504A1 - Double-excitation rotating electrical machine e.g. electric traction motor of electric vehicle, has excitation coils inserted in radial polar teeth, where width of polar teeth is in specific range - Google Patents

Abstract

The machine (1) has permanent magnets (PM) regularly arranged in a circumferential part of a magnetic mass of a rotor (11) to define circumferential polar sections. Excitation coils (EC) are regularly arranged in an intermediate part of the magnetic mass of the rotor. A recess (E3) has maximum width at the level of top of the recess, where the maximum width is about 0.13 mm and 0.44 mm. The coils are inserted in radial polar teeth (RT), where the width of the polar teeth is about 2 and 10 mm.

Description

SYNCHRONOUS ROTOR ELECTRIC MACHINE WITH DOUBLE EXCITATION ROTOR

The present invention relates to a synchronous rotating electrical machine comprising a rotor provided with permanent magnets and an excitation winding. More particularly, the invention relates to a machine of this type for applications as a generator and / or electric traction motor in electric and hybrid motor vehicles. Due to their increased performances in terms of efficiency and mass and volume power, synchronous machines with permanent magnets are now widely used in the field of motor vehicles. In addition, the availability of large-scale rare earth permanent magnets and acceptable economic conditions makes the choice of these electric machines viable for new generations of motor vehicles.

These electric machines are achievable in a wide range of power and speed and find applications in both "all-electric" type vehicles and in low-carbon vehicles of so-called "mild-hybrid" and "full-hybrid" types. (in English terminology). "Mild-hybrid" applications generally concern electrical machines of the order of 8 to 10 KW, for example, an electric motor mounted on the front face of a heat engine and coupled thereto by a transmission belt. It is possible with such an electric motor to reduce the engine capacity of the engine ("engine downsizing" in English terminology) by providing electrical assistance in torque that provides extra power especially during rework. In addition, a traction

low speed, for example in urban environment, can also be provided by the same electric motor. "Full-hybrid" type applications generally concern motors from 30 to 50 kW for series and / or parallel type architectures with a more advanced integration level of the electric motor or motors in the vehicle's power train. However, electric machines excited solely by permanent magnets have problems of defluxing. Except, in a motor vehicle, when the electric machine is used as a traction motor on various vehicle traffic missions, the latter must be able to operate at variable load and speed regimes and must therefore be defluxable to reach the area of the vehicle. high speeds. The double excitation machines are more easily defluxable and offer the possibility of combining in their rotor a high energy density provided by the permanent magnets and an ability to control the magnetic flux in the gap provided by the excitation coil. An interesting structure of double excitation machine is disclosed in the article by Li Li et al. entitled "Some frame reaction compensation methods, numerical design of experiments and optimization for a hybrid excitation machine" and published in IEMDC, Miami, USA (2009). The present invention provides synchronous rotating electrical machines with double excitation with a rotor topology of the type disclosed in the above article and whose design has been optimized to increase the performance and interest of these machines for automobile industry.

According to a first aspect, the present invention relates to a dual excitation electrical rotating machine comprising a stator provided with stator windings and a rotor comprising a plurality of alternating north poles and south poles which are formed from a plurality of permanent magnets and a plurality of excitation coils. The permanent magnets are housed in respective first recessions extending axially and regularly distributed in a circumferential portion of the magnetic mass of the rotor so as to define a plurality of circumferential pole sections. The excitation coils are housed in respective second recessions extending axially and regularly distributed in an intermediate portion of the magnetic mass of the rotor, the intermediate portion being located between the circumferential portion and a central portion of the rotor. Each excitation coil is inserted into a respective radial pole tooth forming a partition between two consecutive second recesses, each pole tooth being substantially aligned on a central radial axis of the corresponding pole. According to the invention, at least one circumferential pole section comprises a third recess substantially aligned with the central radial axis and having a maximum width at a vertex thereof and a minimum width at a foot of it, the foot being the end of the third recess closest to a central portion of the rotor, and the pole tooth has a width of between about 2 mm and about 10 mm and the maximum width of the third recess has a value from about 0.13 mm to about 0.44 mm. Preferably, for obtaining the combined effect of an increase in torque and a reduction

inertia, the radial pole tooth has a width of between about 4 mm and about 6.5 mm and the maximum width of the third recess has a value between about 0.22 mm and about 0.29 mm. According to another particular characteristic of the invention, the minimum width of the third recess is between about 0.8 times a minimum gap width of the machine and about 1.2 times the minimum gap width. According to yet another particular feature of the invention, the circumferential pole section comprising the third recess comprises, between the apex of the third recess and an outer pole face, a portion of magnetic bridge mass having a height of between about 0.7. mm and about 2 mm. According to a particular embodiment of the invention, the third recess extends in the polar tooth. For example, the third recess may extend substantially the full height of the pole tooth. The third recess can advantageously be made in a flared shape. According to yet another particular characteristic of the invention, a ratio of the polar tooth width to the permanent magnet height is between about 0.65 and about 1. The The rotary electric machine according to the invention can advantageously be embodied in the form of an electric motor, a generator or an engine / generator for a motor vehicle. Other features and advantages of the invention will be apparent from the following description of several particular embodiments, with reference to the figures below, in which:

- Fig.1 is a sectional view showing, in a simplified manner, the structure of a particular embodiment of a rotary electric machine with double excitation according to the invention; - Figs.2A and 2B are partial sectional views of the rotor of the machine showing the operation of the double excitation; - Figs.3A and 3B are partial sectional views of the rotor of the machine showing first and second embodiments of a substantially flared shaped recess formed in a circumferential portion of the magnetic mass of the rotor; FIG. 4 shows curves of torque C and of inertia I as a function of a maximum width Lh of recess and a width Ln of polar tooth; - Fig.5 is a partial sectional view of the rotor of the machine in which are defined the width Ln of the pole teeth and a height Hm of the permanent magnets; and Fig. 6 is a power curve of the machine as a function of a ratio Ln / Hm of the pole tooth width to the permanent magnet height. FIG. 1 shows the structure of a particular embodiment 1 of a rotary electric machine with double excitation according to the invention which comprises a stator 10 and a rotor 11. The rotor 11 of the machine 1 comprises a plurality of poles projectors, alternating north and south, which are formed from a plurality of PM permanent magnets and a plurality of EC excitation coils. A concrete embodiment of such a machine according to the invention is for example a motor / generator of 8 to 10 KW for applications in motor vehicles of the type called "mild-hybrid". In its motor mode of operation, such a machine can be

designed for the starting of the engine, the torque assist of the engine as well as for the low-speed electrical traction of the vehicle. In its generator mode, the machine can operate in a normal alternator mode or in a regenerative braking mode. A particular embodiment of this machine comprises a stator 10 having 72 notches 101 and a rotor 11 having 12 alternating north and south poles. The rotor 11 has a diameter of about 100 mm and an axial length of about 50 mm. The rotor 11 comprises 12 PM permanent magnets having a substantially rectangular shape and for dimensions: length x height x width = 50 mm × 5 mm × 6 mm. The stator 10 and the rotor 11 are made conventionally with packets of metal sheets forming magnetic masses. The notches 101 of the stator 10 are provided to receive stator windings (not shown) and form between them a plurality of stator teeth. According to the embodiments, the notches 101 will be provided to house concentrated windings, wound on large teeth, or distributed windings.

The rotor 11 has the general shape of a multilobed cylinder, each of the lobes corresponding to a magnetic pole of the rotor. The magnets PM are disposed buried in the circumferential portion of the rotor 11 and extend axially over the entire length of the rotor 11. The magnets PM are housed in respective recesses E1 and are distributed in the circumferential portion of the rotor 11 in such a manner that two consecutive PM magnets, in the circumferential direction, are arranged with different polar orientations, as appears in FIG. By

For example, if PM1 and PM2 are consecutive magnets, the respective polar orientations may be N-S and S-N or else S-N and N-S, always in the same circumferential direction.

PM magnets are preferably permanent magnets comprising rare earths such as Neodymium-Iron-Boron (NeFeB), Samarium-Iron (SmFe), Samarium-Cobalt (SmCo) magnets or magnets obtained from ferrites. sintered or bound.

The rotor 11 comprises a central bore opening at its two end faces and intended to receive its drive shaft A. It will be noted that in the present invention the shaft A may be made of a magnetic material. In addition to the recesses E1 containing the magnets PM, the rotor 11 also comprises recesses E2 and E3 which are repeated for each pole and extend axially over substantially the entire length of the rotor. The recesses E2 are provided for accommodating excitation coils EC in the rotor 11. The recesses E2 are located under the magnets PM, with as much recess E2 as magnets PM. Two consecutive recesses E2 are separated by a radial polar tooth partition RT around which is wound a corresponding EC excitation coil. The excitation coils EC can be electrically connected in series, parallel or series / parallel assemblies. The E3 recesses fulfill several functions. In general, their main function is to contribute to the control of the magnetic flux and to reduce the inertia of the rotor. Depending on the application, the E3 recesses will have to be optimized by simulations on magnetic field lines in order to find the best possible compromise between a minimum rotor inertia and a maximum mechanical torque delivered by the machine in motor mode. E3 recesses can also be optimized

in order to improve the behavior of the machine vis-à-vis the armature magnetic reaction. It will be noted that certain recesses E2 may advantageously be used for assembly tie rods of the rotor 11. In this embodiment, the recesses E3 contain air. In some applications, they may be filled with non-magnetic materials, even magnetic but with low density. The recesses E3 are arranged here substantially radially in the rotor 11, between two consecutive PM magnets and aligned on a central radial axis of the pole, axis designated conventionally "axis q". Referring to Figs.2A and 2B, the operation of the double excitation at a pole of the rotor 11 is now described, knowing that this operation is identical for all the poles of the rotor 11. Fig.2A shows the case where the excitation coil EC is not excited, which means that it is not traversed by any excitation current. As shown in FIG. 2A, magnetic flux F1 generated by the permanent magnets PM then loop through the magnetic mass of the rotor 11. The reluctance of the magnetic circuits of the rotor 11 must of course be determined so as to avoid any demagnetization of the magnets. permanent PM. In this mode of operation, given that the magnetic flux F1 does not pass through the stator 10, it follows that no electromotive force (f.e.m) is produced in the stator windings.

Fig.2B shows the case where the excitation coil EC is excited, which means that it is traversed by an excitation current. The schematic representation of FIG. 2B corresponds to the case where the excitation current passing through the coil EC has an intensity such that the magnetic fluxes generated by the magnets PM are constrained by

all to flow through the stator 10 (magnetic flux F1 '). The excitation current flowing through the coil EC causes the appearance of an additional magnetic flux at the corresponding polar tooth RT. This additional flow is subdivided into two parts F21 and F22 which pass on either side of the recess E3 and then circulate in the stator 10. As appears in FIG. 2B, the looping of the flows F21 and F22 towards the Polar tooth RT concerned is through the neighboring RT pole teeth, located on both sides of the concerned one. Referring to Figs.3A and 3B, the recess E3 is now described in more detail. As shown in Figs.3A and 3B, in this embodiment, the recess E3 has a substantially flared shape. The flared portion is located in the circumferential portion of the rotor 11. Of course, shapes other than this flared shape are possible for the recess E3 and remain within the scope of the present invention, the flared shape described herein being given only as an exemplary embodiment. The following parameters must be taken into account to define the recess E3, namely: Lb, which is the minimum width of the recess E3 at one foot thereof; - Hp which is the height of sheet remaining between the top of the recess E3 and the outer face of the corresponding pole, height Hp referred to as "bridge height" below; - Pe which is the depth of the recess E3; Lh which is the maximum width of the recess E3 at a vertex thereof; and - Ln which is the width of the polar tooth RT. The simulations and tests carried out by the inventive entity have shown that the minimum recess width parameter Lb must be determined according to the width

between the rotor 11 and the stator 10. In the embodiments described here, the gap between the rotor 11 and the stator 10 is variable due to the multi-lobed structure of the rotor 11. The gap width e (shown in Fig.3A) is the minimum width of the gap, that is to say, the gap width at the axis q. It should be noted here that the variability of the air gap contributes to a reduction of harmonics and therefore iron losses. The inventive entity has demonstrated that the minimum recess width Lb must remain substantially equivalent to the gap width e. In fact, a width Lb that is too high leads to a magnetic saturation of the pole and, consequently, to a reduction in the mechanical torque. Preferably, the minimum recess width Lb should be between about 0.8 times the gap width e (0.8 x e) and about 1.2 times the gap width e (1.2 x e). The bridge height Hp must be minimized to obtain a magnetic saturation which, by blocking the magnetic flux along the axis q, causes an increase in the torque. The reduction of the height Hp is also favorable to a significant reduction of the inertia. Given that the inertia is proportional to the square of the radius, any withdrawal of mass as far as possible from the center of the rotor is very favorable to the reduction of inertia. However, this bridge height Hp must be dimensioned in such a way that the bridge can withstand the mechanical stresses to which the rotor is subjected, in particular the centrifugal force. The bridge height Hp can not be less than a minimum value that is imposed by these mechanical stresses. The tests performed by the inventive entity have shown that a bridge width Hp of between about 0.7 mm and about 2 mm is a good compromise. Concerning the depth Pe of the recess E3, Figs. 3A and 3B show two possible embodiments.

In the embodiment of Fig.3A, the bottom of the foot of the recess E3 is at a high rounded corner CAh of the recess E2. In some applications, saturation zones ZS1 between the bottom of the foot of the recess E3 and the rounded high corner CAh of the recess E2 may be dimmensionées so as to control the magnetic flux. In the embodiment of Fig.3B, the recess E3 extends substantially over the entire height of the pole tooth RT. The bottom of the foot of the recess E3 is at a low rounded corner CAb of the recess E2. In a similar manner to the embodiment of FIG. 3A, saturation zones ZS2 between the bottom of the foot of the recess E3 and the rounded high corner CAb of the recess E2 can be dimmensioned in order to control the magnetic flux. It will be noted here that the width Ln 'of the polar tooth RT will be greater than that Ln of the embodiment of FIG. 3A in order to maintain the same magnetic mass width for the tooth RT.

According to the invention, the maximum width Lh of the recess E3 is dimensioned as a function of Ln which is the width of the polar tooth RT, so as to optimize the compromise between inertia and torque. In FIG. 4, curves of torque C and of inertia I are shown as a function of the maximum recess width Lh and the width Ln of the polar tooth RT. The torque curve is represented with square shaped dots. The inertia curve is represented with diamond-shaped dots.

From the study of these curves, it appears that a good compromise between inertia and torque can be found for Ln and Lh values of between about 2 and about 10 mm and between about 0.13 and about 0, 44 mm, respectively. It will be noted that for values of Ln and Lh comprised respectively between 4 and 6.5 mm and 0.22 and 0.29,

it is possible both to reduce the inertia and increase the torque. Given the above teaching by the inventive entity, the skilled person will choose in the given intervals the values (Ln, Lb) best suited to the intended application. Referring to Figs.6 and 7, it is now discussed an optimization proposed by the inventive entity of the ratio between the width Ln of the pole teeth RT and the height Hm of the permanent magnets PM. The tests and simulation performed by the inventive entity have shown that this is a critical point in the design of the machine, which has a significant influence on the power of the latter. A compromise must be found between the percentage of magnetic flux produced by the permanent magnets and that produced by the excitation winding, in other words, between the permanent magnets and the amount of copper integrated in the rotor. The parameter Hm is here representative of the magnetic flux produced by the magnets. The parameter Ln is related to the quantity of copper in the rotor and therefore to the magnetic flux produced by the excitation coil. Indeed, according to the width Ln of the pole teeth, it will be possible to include more or less copper in the recesses E2. In addition, the width Ln is to be dimensioned carefully so as to avoid, on the one hand, insufficient solicitation of the magnetic mass of the polar tooth RT with an operating point of the magnetic circuit which is too far from the magnetic saturation and on the other hand, excessive saturation of the magnetic mass of the polar tooth RT which would limit the passage of the magnetic flux generated by the excitation coil. The curve of FIG. 7, taken up by the inventive entity, gives the power P of the machine as a function of the value of the ratio Ln / Hm. An Ln / Hm ratio of between approximately 0.65 and approximately 1 proves to be a good compromise and guarantees the machine's performance.

Claims (10)

REVENDICATIONS1. A dual excitation electrical rotating machine comprising a stator (10) having stator windings and a rotor (11) comprising a plurality of alternating north and south poles which are formed from a plurality of permanent magnets (PM) and a plurality of excitation coils (EC), said permanent magnets (PM) being accommodated in respective first recesses (E1) extending axially and regularly distributed in a circumferential portion of the magnetic mass of said rotor (11) so as to defining a plurality of circumferential pole sections, said excitation coils (EC) being housed in respective second recesses (E2) extending axially and regularly distributed in an intermediate portion of the magnetic mass of said rotor (11), said intermediate portion being located between said circumferential portion and a central portion (A) of said rotor (11), each said excitation coil (EC) being inserted into a respective radial pole tooth (RT) forming a partition between two said second consecutive recesses (E2), each pole tooth (RT) being substantially aligned on a central radial axis (q) of the corresponding pole, characterized in that at least one said circumferential pole section comprises a third recess (E3) substantially aligned with said central radial axis (q) and having a maximum width (Lh) at a vertex thereof and a minimum width (Lb) at the one foot thereof, said foot being the end of the third recess (E3) closest to a central portion (A) of said rotor, and said polar tooth (RT) has a width (Ln) between about 2 mm and about 10 mm and said maximum width (Lh) of said third recess (E3) has a value between about 0.13 mm and about 0.44 mm. Rotary electric machine according to claim 1, characterized in that said polar tooth (RT) has a width (Ln) of between about 4 mm and about 6.5 mm and said maximum width (Lh) of said third recess (E3). has a value between about 0.22 mm and about 0.29 mm. 3. A rotary electric machine according to claim 1 or 2, characterized in that said minimum width (Lb) of said third recess (E3) is between about 0.8 times a minimum air gap width (e) of the machine and about 1.2 times said minimum gap width. 4. rotary electric machine according to any one of claims 1 to 3, characterized in that said circumferential pole section comprising said third recess (E3) comprises, between said apex of said third recess (E3) and an outer pole face, a portion bridge magnetic mass having a height (Hp) of between about 0.7 mm and about 2 mm. 5. The rotary electric machine as claimed in claim 1, wherein said third recess extends in said polar tooth. 6. rotary electric machine according to claim 5, characterized in that said third recess (E3) extends substantially over the entire height of said pole tooth (RT). 7. rotary electric machine according to any one of claims 1 to 6, characterized in that said third recess (E3) has a flared shape 8. rotary electric machine according to any one of claims 1 to 7, characterized in that a ratio (Ln / Hm) of the pole tooth width (Ln) on the permanent magnet height (Hm) is between about 0.65 and about 1. 9. rotary electric machine according to any one of claims 1 to 8, characterized in that it is performed in the form of an electric motor for a motor vehicle. 10. Rotating electrical machine according to any one of claims 1 to 8, characterized in that it is performed in the form of an electric generator or a motor / generator for a motor vehicle.